1. Field of the Invention
The present invention relates to a die-height adjusting device of mechanical press such as a crank press and a knuckle joint press, etc.
As for a basic construction of such a die-height adjusting device has so far been generally known the following one.
That is, a slide of a mechanical press is interlockingly connected to a prime mover through a slide actuating mechanism. At the part of the press between the slide actuating means supported by a frame and an output end portion of the slide, there is provided an extendible and contractible device for the adjustment of the die-height, which is adapted to be adjustably actuated and stopped in the extending and contracting direction thereof by means of an operating device for the extension and the contraction adjustment thereof.
As known well in the art, at each coupling portion in this basic construction, there is provided a clearance for a movement thereof, which may be gathered so as to form a total clearance. During a punching operation of the mechanical press, the frame of the press is resiliently deformed by a reaction force which is generated when a punch performs a punching for a work plate, and the slide is struck out abruptly by a restorative resilient force of the frame through the slide actuating mechanism at the time of breakthrough thereof just afer the punching is performed. At that time, a collision is caused at the every portion forming the total clearance so as to cause noises of shock, abrasions and deformations.
The concrete construction of the die-height adjusting device which is known by the inventor of the present invention will be described with reference to FIGS. 7 and 8 hereinafter.
In FIGS. 7 and 8, the symbol 204 is a slide, 208 is a slide actuating mechanism, and 218 is an extendible and contractible device for the adjustment of the die-height. And in the intermediate portion of a connecting rod 224, there is provided a height-adjusting screw means 280 which comprises a female screw 281 provided in a big end portion 225 of the connecting rod 224 and a male screw 282 provided on the small end portion 226 thereof so as to be threadably mounted to the female screw 281.
The conventional basic construction functions as follows.
When a die-height adjustment is required, the die-height is adjusted by the upward and downward movement of the slide 204 in the height direction which is controlled by the length adjustment of the connecting rod 224 carried out by rotating the small end portion 226 through a gearing mechanism 283 by an electric motor 241 for the height adjustment, which constitutes an extendible and contractible device 219 for the adjustment of the die-height. On the other hand, during the work of press, the force of press is transmitted to the slide 204 through the height-adjusting screw means 280 and the small end portion 226 of the connecting rod from the big end portion 225 of the connecting rod so that the punching is carried out for the work plate by a die-set one of which is detachably fixed to the output end portion 217 of the slide 204.
Even though the above-mentioned prior art has an advantage that the die-height can be adjusted readily, there are, however, the following disadvantages associated therewith.
(1) Noises made by the mechanical press is very large.
As shown in FIG. 8, in order to rotate the small end portion 226 smoothly by the electric motor 241 for the height adjustment, it is necessary to provide a clearance (e) for a screw engagement between the female screw 281 and the male screw 282. And since the height-adjusting screw means 280 is enlarged in their diameters in order to transmit a force of press, the clearance (e) for the screw engagement also gets enlarged.
Moreover, since the die-height adjustment is carried out in the cold condition of the mechanical press before its operation and the press is expanded in the hot condition thereof at the normal operation of the punching process, the clearance (e) gets further enlarged.
The large clearance (e) for the screw engagement makes the above-mentioned total clearance larger in the slide actuating mechanism 208. As the result, the enlarged total clearance tends to make shock noises, abrasions and deformations larger at the time of breakthrough.
(2) The electric motor for the height adjustment becomes large.
Since the height-adjusting screw means 280 of a large diameter is required for the transmission of the force of press, a friction resistance gets large at the operation of the press and the transmission efficiency gets lowered. Therefore, it becomes necessary to mount a large electric motor 241 for the height adjustment and an energy loss gets also increased.
In the case that a pre-load is applied by the electric motor 241 when the die-set is mounted onto the mechanical press, a larger electric motor 241 is required in compensation for the low transmission efficiency of the height-adjusting screw means 280 and an energy loss also gets more increased.